A method is provided for forming SRAM cells with low energy implants. Embodiments include forming deep trenches in a silicon substrate; forming a deep n-well or deep p-well around a bottom of each deep trench; filling the deep trenches with oxide; forming a first or second shallow trench between each pair of adjacent deep trenches; forming a first p-well or first n-well, respectively, above each deep n-well or p-well; forming a second n-well at a bottom of each first shallow trench; forming a p+ region above each second n-well on each side of each first shallow trench; filling the first shallow trenches with oxide; forming a second p-well at a bottom of each second shallow trench; filling the second shallow trenches with oxide; forming a p+ region above each second n-well on each side of each first shallow trench; and forming an n+ region above each second p-well.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method of comprising: forming a plurality of deep trenches having a first depth in a silicon substrate; forming a deep n-well or deep p-well around a bottom of each of the plurality of deep trenches; filling the plurality of deep trenches with a first oxide; forming a first or second shallow trench between each pair of adjacent deep trenches, each first and second shallow trench having a second depth less than the first depth; forming a first p-well or first n-well, respectively, above each deep n-well or p-well; forming a second n-well at a bottom of each first shallow trench; filling the first shallow trenches with a second oxide; forming a second p-well at a bottom of each second shallow trench; filling the second shallow trenches with the second oxide; forming a p+ region above each second n-well on each side of each first shallow trench; and forming an n+ region above each second p-well on each side of each second shallow trench.
2. The method according to claim 1 , comprising forming the plurality of deep trenches to a depth of 1500 angstroms (Å) to 5000 Å.
3. The method according to claim 1 , comprising forming the plurality of deep trenches by etching with sulfur hexafluoride (SF 6 ) or nitrogen trifluoride (NF 3 ).
4. The method according to claim 1 comprising forming the first p-well or first n-well, respectively, above each deep n-well or p-well by implanting a p-type or n-type dopant with an energy of 5 kiloelectron volts (keV) to 80 keV.
5. The method according to claim 1 , comprising forming the first and second shallow trenches between the deep trenches by: forming a self-aligned hardmask over the silicon substrate; and etching the first and second shallow trenches through openings in the self-aligned hardmask to a depth of 700 Å to 3000 Å.
6. The method according to claim 5 , comprising forming the hardmask in a self aligned way by depositing high aspect ratio process (HARP) material, TEOS, polysilicon and/or nitride as layers and forming spacers.
7. The method according to claim 5 , comprising etching the first and second shallow trenches to form a silicon fin between each deep trench and each adjacent first and second shallow trench, the silicon fins having a pitch of 40 (nanometers) nm to 100 nm.
8. The method according to claim 7 , comprising etching the first and second shallow trenches to form silicon fins each having a width of 8 nm to 50 nm.
9. The method according to claim 7 , comprising forming each second n-well or second p-well by: covering each second or first shallow trench, respectively, and adjacent silicon fins with a photomask; and implanting n-type or p-type dopants through the bottom of each first or second shallow trench, respectively, at an energy level of 10 keV to 30 keV.
10. The method according to claim 9 , comprising doping silicon fins adjacent opposite sides of each first or second shallow trench through a mask with p+ or n+ dopants, respectively, to a depth of 50 Å to 1000 Å, after filling the second shallow trenches.
11. The method according to claim 9 , comprising forming the photomask with openings having a width of 80 nm.
12. The method according to claim 11 , comprising forming the photomask by allowing for misalignment of ½ trench plus fin width.
13. The method according to claim 1 , comprising heating the first and second oxides in a high temperature environment for a duration that is sufficient to cause densification of the first and second oxides.
14. The method according to claim 1 , comprising forming four first shallow trenches and two second shallow trenches to form a static random-access memory (SRAM) cell comprising at least four n-type metal-oxide-semiconductor (NMOS) field effect transistors and at least two p-type metal-oxide-semiconductor (PMOS) field effect transistors.
15. A method of comprising: forming a plurality of deep trenches having a depth of 1500 Å to 5000 Å in a silicon (Si) substrate; forming a deep n-well or a deep p-well across the Si substrate through the plurality of deep trenches; filling each of the plurality of deep trenches with the first oxide; forming a plurality of first and second shallow trenches having a depth of 700 Å to 3000 Å in the Si substrate, each pair of adjacent deep trenches having one first or second shallow trench therebetween; forming a first p-well or first n-well, respectively, above the deep n-well or deep p-well; forming a first photoresist over the second shallow trenches and adjacent Si substrate; forming a second n-well through a bottom of each first shallow trench; filling each first shallow trench with a second oxide; removing the first photoresist; forming a second photoresist over the first shallow trenches and adjacent Si substrate; forming a second p-well through a bottom of each second shallow trench; filling each second shallow trench with the second oxide; removing the second photoresist; forming a p+ region above each second n-well on each side of each first shallow trench through a first mask; and forming an n+ region above each second p-well on each side of each second shallow trench through a second mask.
16. The method according to claim 15 , comprising heating the first and second oxides at a temperature and for a duration sufficient to cause densification of the first and second oxides prior to forming the p+ regions and n+ regions.
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October 30, 2012
February 3, 2015
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